Re: [PATCH 19/19] gpio: add GPIO controller found on Waveshare DSI TOUCH panels

Bartosz Golaszewski
2026-04-03T12:30:25Z

On Wed, 1 Apr 2026 09:26:38 +0200, Dmitry Baryshkov
<dmitry.baryshkov@oss.qualcomm.com> said:
> The Waveshare DSI TOUCH family of panels has separate on-board GPIO
> controller, which controls power supplies to the panel and the touch
> screen and provides reset pins for both the panel and the touchscreen.
> Also it provides a simple PWM controller for panel backlight. Add
> support for this GPIO controller.
>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
> drivers/gpio/Kconfig | 10 ++
> drivers/gpio/Makefile | 1 +
> drivers/gpio/gpio-waveshare-dsi.c | 220 ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 231 insertions(+)
>
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index 4c3f6ec336c1..f0bb5cdebf9b 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -804,6 +804,16 @@ config GPIO_VISCONTI
> help
> Say yes here to support GPIO on Tohisba Visconti.
>
> +config GPIO_WAVESHARE_DSI_TOUCH
> + tristate "Waveshare GPIO controller for DSI panels"
> + depends on BACKLIGHT_CLASS_DEVICE
> + depends on I2C
> + select REGMAP_I2C
> + help
> + Enable support for the GPIO and PWM controller found on Waveshare DSI
> + TOUCH panel kits. It provides GPIOs (used for regulator control and
> + resets) and backlight support.
> +
> config GPIO_WCD934X
> tristate "Qualcomm Technologies Inc WCD9340/WCD9341 GPIO controller driver"
> depends on MFD_WCD934X
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index 20d4a57afdaa..75ce89fc3b93 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -207,6 +207,7 @@ obj-$(CONFIG_GPIO_VIRTUSER) += gpio-virtuser.o
> obj-$(CONFIG_GPIO_VIRTIO) += gpio-virtio.o
> obj-$(CONFIG_GPIO_VISCONTI) += gpio-visconti.o
> obj-$(CONFIG_GPIO_VX855) += gpio-vx855.o
> +obj-$(CONFIG_GPIO_WAVESHARE_DSI_TOUCH) += gpio-waveshare-dsi.o
> obj-$(CONFIG_GPIO_WCD934X) += gpio-wcd934x.o
> obj-$(CONFIG_GPIO_WHISKEY_COVE) += gpio-wcove.o
> obj-$(CONFIG_GPIO_WINBOND) += gpio-winbond.o
> diff --git a/drivers/gpio/gpio-waveshare-dsi.c b/drivers/gpio/gpio-waveshare-dsi.c
> new file mode 100644
> index 000000000000..30fe7569c150
> --- /dev/null
> +++ b/drivers/gpio/gpio-waveshare-dsi.c
> @@ -0,0 +1,220 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 Waveshare International Limited
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#include <linux/backlight.h>
> +#include <linux/err.h>
> +#include <linux/fb.h>
> +#include <linux/gpio/driver.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/regmap.h>
> +
> +/* I2C registers of the microcontroller. */
> +#define REG_TP 0x94
> +#define REG_LCD 0x95
> +#define REG_PWM 0x96
> +#define REG_SIZE 0x97
> +#define REG_ID 0x98
> +#define REG_VERSION 0x99
> +
> +enum {
> + GPIO_AVDD = 0,
> + GPIO_PANEL_RESET = 1,
> + GPIO_BL_ENABLE = 2,
> + GPIO_IOVCC = 4,
> + GPIO_VCC = 8,
> + GPIO_TS_RESET = 9,
> + NUM_GPIO = 16,

Why is this part of an enum?

> +};
> +
> +struct waveshare_gpio {
> + struct mutex dir_lock;
> + struct mutex pwr_lock;
> + struct regmap *regmap;
> + u16 poweron_state;
> +
> + struct gpio_chip gc;
> +};
> +
> +static const struct regmap_config waveshare_gpio_regmap_config = {
> + .reg_bits = 8,
> + .val_bits = 8,
> + .max_register = REG_PWM,
> +};
> +
> +static int waveshare_gpio_get(struct waveshare_gpio *state, unsigned int offset)
> +{
> + u16 pwr_state;
> +
> + mutex_lock(&state->pwr_lock);
> + pwr_state = state->poweron_state & BIT(offset);
> + mutex_unlock(&state->pwr_lock);
> +
> + return !!pwr_state;
> +}
> +
> +static int waveshare_gpio_set(struct waveshare_gpio *state, unsigned int offset, int value)
> +{
> + u16 last_val;
> +
> + mutex_lock(&state->pwr_lock);

Can you use guards for locks?

> +
> + last_val = state->poweron_state;
> + if (value)
> + last_val |= BIT(offset);
> + else
> + last_val &= ~BIT(offset);
> +
> + state->poweron_state = last_val;
> +
> + regmap_write(state->regmap, REG_TP, last_val >> 8);
> + regmap_write(state->regmap, REG_LCD, last_val & 0xff);

I2C regmap writes can fail and their return value should be checked.

> +
> + mutex_unlock(&state->pwr_lock);
> +
> + return 0;
> +}
> +
> +static int waveshare_gpio_gpio_get_direction(struct gpio_chip *gc, unsigned int offset)
> +{
> + return GPIO_LINE_DIRECTION_OUT;
> +}
> +
> +static int waveshare_gpio_gpio_get(struct gpio_chip *gc, unsigned int offset)
> +{
> + struct waveshare_gpio *state = gpiochip_get_data(gc);
> +
> + return waveshare_gpio_get(state, offset);
> +}
> +
> +static int waveshare_gpio_gpio_set(struct gpio_chip *gc, unsigned int offset, int value)
> +{
> + struct waveshare_gpio *state = gpiochip_get_data(gc);
> +
> + return waveshare_gpio_set(state, offset, value);
> +}
> +
> +static int waveshare_gpio_update_status(struct backlight_device *bl)
> +{
> + struct waveshare_gpio *state = bl_get_data(bl);
> + int brightness = backlight_get_brightness(bl);
> +
> + waveshare_gpio_set(state, GPIO_BL_ENABLE, brightness);
> +
> + return regmap_write(state->regmap, REG_PWM, brightness);
> +}
> +
> +static const struct backlight_ops waveshare_gpio_bl = {
> + .update_status = waveshare_gpio_update_status,
> +};
> +
> +static int waveshare_gpio_i2c_read(struct i2c_client *client, u8 reg, unsigned int *buf)
> +{
> + int val;
> +
> + val = i2c_smbus_read_byte_data(client, reg);
> + if (val < 0)
> + return val;
> +
> + *buf = val;
> +
> + return 0;
> +}
> +
> +static int waveshare_gpio_probe(struct i2c_client *i2c)
> +{
> + struct backlight_properties props = {};
> + struct waveshare_gpio *state;
> + struct device *dev = &i2c->dev;
> + struct backlight_device *bl;
> + struct regmap *regmap;
> + unsigned int data;
> + int ret;
> +
> + state = devm_kzalloc(dev, sizeof(*state), GFP_KERNEL);
> + if (!state)
> + return -ENOMEM;
> +
> + ret = devm_mutex_init(dev, &state->dir_lock);
> + if (ret)
> + return ret;
> +
> + ret = devm_mutex_init(dev, &state->pwr_lock);
> + if (ret)
> + return ret;
> +
> + i2c_set_clientdata(i2c, state);
> +
> + regmap = devm_regmap_init_i2c(i2c, &waveshare_gpio_regmap_config);
> + if (IS_ERR(regmap))
> + return dev_err_probe(dev, PTR_ERR(regmap), "Failed to allocate register map\n");
> +
> + ret = waveshare_gpio_i2c_read(i2c, REG_ID, &data);
> + if (ret < 0)
> + return dev_err_probe(dev, ret, "Failed to read register\n");
> +
> + dev_dbg(dev, "waveshare panel hw id = 0x%x\n", data);
> +
> + ret = waveshare_gpio_i2c_read(i2c, REG_SIZE, &data);
> + if (ret < 0)
> + return dev_err_probe(dev, ret, "Failed to read register\n");
> +
> + dev_dbg(dev, "waveshare panel size = %d\n", data);
> +
> + ret = waveshare_gpio_i2c_read(i2c, REG_VERSION, &data);
> + if (ret < 0)
> + return dev_err_probe(dev, ret, "Failed to read register\n");
> +
> + dev_dbg(dev, "waveshare panel mcu version = 0x%x\n", data);
> +
> + state->poweron_state = BIT(GPIO_TS_RESET);
> + regmap_write(regmap, REG_TP, state->poweron_state >> 8);
> + regmap_write(regmap, REG_LCD, state->poweron_state & 0xff);
> + msleep(20);
> +
> + state->regmap = regmap;
> + state->gc.parent = dev;
> + state->gc.label = i2c->name;
> + state->gc.owner = THIS_MODULE;
> + state->gc.base = -1;
> + state->gc.ngpio = NUM_GPIO;
> +
> + /* it is output only */
> + state->gc.get = waveshare_gpio_gpio_get;
> + state->gc.set = waveshare_gpio_gpio_set;
> + state->gc.get_direction = waveshare_gpio_gpio_get_direction;
> + state->gc.can_sleep = true;
> +
> + ret = devm_gpiochip_add_data(dev, &state->gc, state);
> + if (ret)
> + return dev_err_probe(dev, ret, "Failed to create gpiochip\n");
> +

This driver looks like it could be easily converted to use gpio-regmap and
become much shorter in the process. Could you please take a look at
linux/gpio/regmap.h?

> + props.type = BACKLIGHT_RAW;
> + props.max_brightness = 255;
> + props.brightness = 255;
> + bl = devm_backlight_device_register(dev, dev_name(dev), dev, state,
> + &waveshare_gpio_bl, &props);
> + return PTR_ERR_OR_ZERO(bl);
> +}
> +
> +static const struct of_device_id waveshare_gpio_dt_ids[] = {
> + { .compatible = "waveshare,dsi-touch-gpio" },
> + {},
> +};
> +MODULE_DEVICE_TABLE(of, waveshare_gpio_dt_ids);
> +
> +static struct i2c_driver waveshare_gpio_regulator_driver = {
> + .driver = {
> + .name = "waveshare-regulator",
> + .of_match_table = of_match_ptr(waveshare_gpio_dt_ids),
> + },
> + .probe = waveshare_gpio_probe,
> +};
> +
> +module_i2c_driver(waveshare_gpio_regulator_driver);
> +
> +MODULE_DESCRIPTION("GPIO controller driver for Waveshare DSI touch panels");
> +MODULE_LICENSE("GPL");
>
> --
> 2.47.3
>
>

Bart